Question

Fructose is found in many fruits. From memory, draw fructose in

1. the Fischer projection of the open chain.
2. The most stable chair conformation of the most stable pyranose anomer.
3. The Haworth projection of the most stable pyranose anomer

Short answer

Fructose is a ketohexose which contain a ketone group. It is used as a sweetening agent in many confectionaries and also as a substitute of cane sugar.

Step-by-step solution

Fructose

Fructose is a ketohexose which contain a ketone group. It is used as a sweetening agent in many confectionaries and also as a substitute of cane sugar.

Pyranose

Pyranose is a six-membered cyclic hemiacetal whose name is derived from the six-membered cyclic ether pyran.

Anomers

The diastereomers resulting from cyclisation are known as anomers. They differ only in the configuration around first carbon (C1) which is referred to as the anomeric carbon (hemiacetal carbon atom).

Identifying α  and β  anomers of pyranoses

For α-anomer, hydroxy group (-OH) on the anomeric carbon is down (axial position) while for β - anomer, hydroxy group (-OH) on the anomeric carbon is up (equatorial position). Again, for anomer, the anomeric hydroxy (-OH) group is placed trans to the terminal -CH₂OH group while for β- anomer, the anomeric hydroxy (-OH) group is placed cis to the terminal -CH₂OH group.

 Step 5: Structure of various forms of fructose

a) Sugars in their open chain form is given by the Fischer projection where the vertical solid lines show the connection of different carbon atoms present in a sugar while the horizontal solid lines show carbon-oxygen and carbon- hydrogen bonds.

b) The most stable chair conformation of the most stable pyranose anomer of fructose is β-D- fructopyranose . In chair conformation of β-D- fructopyranose , the anomeric carbon is C1 . The hydroxy group ( -OH ) on the anomeric carbon is up (equatorial position).

c) The Haworth projection of β-D- fructopyranose is represented by the figure below: